Dental curable composition including chain transfer agent

ABSTRACT

The present invention relates to a dental curable composition that can be suitably used as a dental material that can substitute part or all of a natural tooth, in particular, a resin material for dental cutting and machining in the field of dental care. An object of the present invention is to provide a dental curable composition in which, when a block shape usable as a resin material for dental cutting and machining is produced while mechanical properties such as hardness, bending strength and compressive strength as well as aesthetic property required for a crown prosthetic appliance are maintained, the dental curable composition can be molded and processed with pressure and heating while strain generated in the block is reduced and no cracks and chipping occur. There is provided a dental curable composition including (a) a polymerizable monomer and (b) a filler in a weight ratio of 10:90 to 70:30, and including 0.01 to 10 parts by weight of (c) a polymerization initiator and 0.001 to 1 part by weight of (d) a chain transfer agent being a terpenoid compound based on 100 parts by weight of the polymerizable monomer (a).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a dental curable composition to besuitably used as a dental material that can substitute part or all of anatural tooth, or a resin material for dental cutting and machining, anda resin material for dental cutting and machining, a resin artificialtooth and a composite resin artificial tooth produced by the dentalcurable composition.

2. Description of the Related Art

A resin or a composite obtained by mixing a resin and an inorganicfiller has been conventionally used with being molded into an artificialtooth in one treatment in the field of dentistry. In formation of theartificial tooth, the material of the artificial tooth has been filledin a mold and cured, but strain has been generated in curing to causecracks and chipping to be generated.

In recent years, a dental CAD/CAM system has become widely used, and hasenabled cutting and machining precisely so as to allow a prostheticappliance to be produced. A resin block and a composite resin block,also having flexibility as a material to be cut and machined, are easyin occlusal adjustment and polishing operation at a restorationlaboratory or chair side, and hardly damage an opposing tooth due toabrading of themselves, as compared with a ceramics block. Such a resinblock and a composite resin block have been filled in a mold and curedas in the artificial tooth, however, strain has been generated in curingto cause cracks and chipping to be generated.

Japanese Patent Laid-Open No. 10-323353 discloses a dental resinmaterial including a methacrylate or acrylate monomer and a thermalpolymerization initiator. The (meth)acrylate monomer included in thisdental resin material, however, has a high heat-curing reaction rate,therefore, for example, curing is rapidly initiated near a surface of amolded product, which is in contact with a mold, and volume shrinkagelocally occurs due to polymerization of the monomer, and thus there isthe following problem: strain is generated in a molded product tothereby cause cracks and chipping to occur and a uniform molded productcannot be obtained.

With respect to the resin block and the composite resin block, there hasbeen a demand for a molding technique for producing a material formachining, having a large shape. A large molded product is difficult toproduce as a uniform molded product with no incorporation of gasbubbles, the absence of strain, and no cracks and chips. In particular,methyl methacrylate is low in boiling point and high inpolymerizability, therefore easily causes generation of strain andincorporation of gas bubbles due to foaming, and has also many problemsin terms of productivity, for example, is required to be polymerizedover a long time in order to be uniformly polymerized and cured.

Japanese Patent Laid-Open No. 2012-214398 discloses the following:polyethylene glycol dimethacrylate having a specific molecular weightcan be contained in a specific amount to thereby provide a moldedproduct without generation of cracks and chipping. A resin moldedproduct uniformly thermally cured, however, cannot be obtained, and thefollowing problem is caused: strain is still generated in a moldedproduct to thereby cause cracks and chipping to be generated.

Japanese Patent Laid-Open No. 2011-037726 describes the invention of abactericidal sealer for filling a root canal, in which terpinen-4-ol iscompounded in order to impart the bactericidal effect.

National Publication of International Patent Application No. 2009-541375and National Publication of International Patent Application No.2007-526270 describe a dental material such as a material for anartificial tooth, in which terpinene is compounded as a stabilizer.

While a resin material for dental cutting and machining (resin block),having a large shape, for use in a temporary prosthetic appliance or adenture base is produced by admixing a powder material mainly includingpolymethyl methacrylate with a liquid material mainly including methylmethacrylate, and then filling the resulting admixture into a mold formolding and processing with pressure and heating, such an admixture hasa high thermal conductivity and therefore a portion thereof, beingpresent in the vicinity of the mold, starts to be rapidly polymerized.Therefore, the following problem is caused: strain is generated betweenthe vicinity of the mold and the inside of the mold to cause cracks andchipping to be generated. In addition, since methyl methacrylate is apolymerizable monomer having a low boiling point, there is also thefollowing problem: foaming occurs in the process of a rise in moldtemperature to generate gas bubbles in a molded product.

A resin material for dental cutting and machining (composite resinblock), for producing a temporary prosthetic appliance, a denture baseor the like, has a filler such as a silica filler or anorganic/inorganic composite filler compounded at a high density in orderto exhibit aesthetic property and mechanical properties required for acrown prosthetic appliance. In this case, a material structure isadopted in which a polymerizable monomer is present around the fillerwith being polymerized for curing. While the composite resin block isproduced by, for example, filling a paste-like dental curablecomposition including the filler and the polymerizable monomer into amold for molding and processing with pressure and heating, the fillerand the polymerizable monomer have a largely different thermalconductivity from each other, and therefore the following problem iscaused: micro-strain is generated in the block to cause cracks andchipping. This is because the polymerizable monomer in which heatconducts quickly under pressure and heating for production of the blockis rapidly polymerized. Moreover, in molding and processing in which thepaste-like dental curable composition is pressurized and heated in themold, while heat polymerization instantly progresses in the paste in thevicinity of the mold because of ease of conduction of heat, heatpolymerization slowly progresses in the paste far from the mold andpresent near the inside of the mold, in which heat hardly conducts, ascompared with the former case. Such ununiform progress of heatpolymerization depending on the location of the paste causes thefollowing problem: micro-strain is generated in the block to causecracks and chipping. In addition, when the polymerizable monomer havinga low boiling point, such as methyl methacrylate, is used, there is alsothe following problem: foaming occurs in the process of a rise in moldtemperature to generate gas bubbles in a molded product.

The resin artificial tooth and the composite artificial tooth are madehaving a form similar to a natural tooth by stacking respective layersfor polymerization and curing by a compression molding method in whichraw materials for a paste-like admixture are filled in a mold andpressurized and heated, an injection molding method in which theadmixture is injected as a raw material into a mold at a constantpressure, or the like. The difference in conduction of heat, however, iscaused by, for example, ununiform component compositions and thicknessesof the layers stacked and hence the presence of a thinner portion and athicker portion in the same layer, and furthermore the locationalrelationship (for example, the vicinity of the mold or the inside of themold) from the mold in filling of the admixture into the mold. As aresult, the rate of polymerization and curing is changed, and there isthe following problem: micro/macro-strain is generated to cause defectssuch as partial shrinkage, cracking, clouding and chips in molding withpressure and heating. In addition, when the respective layers aresequentially stacked with polymerization and curing, there is also thefollowing problem: adhesiveness between the layers is insufficient dueto the influences of compatibility in pressure-welding of a raw materialfor providing a new layer with polymerization and curing, to the surfaceof the layer cured, and of the polymerization shrinkage stress in thepolymerization and curing, and physical properties intended are notexhibited.

Furthermore, a monofunctional (meth)acrylate monomer to be mainly usedas a component of the resin artificial tooth has a low boiling point andtherefore is to be foamed by a rapid rise of temperature to cause gasbubbles to be easily incorporated in polymerization and curing. Thereare also many problems in terms of productivity, for example,polymerization and curing are required to be performed over a longperiod of time in order to achieve uniform polymerization and curing.

From the foregoing, an object of the present invention is to provide adental curable composition in which, when a block-shaped or disc-shapedmolded product usable as a resin material for dental cutting andmachining is produced while mechanical properties such as hardness,bending strength and compressive strength as well as aesthetic propertyrequired for a temporary prosthetic appliance, a denture base and acrown prosthetic appliance are maintained, the dental curablecomposition can be molded and processed with pressure and heating whilestrain generated in the molded product is reduced, no cracks andchipping occur, and no gas bubbles are incorporated due to foaming.

Another object of the present invention is to provide a resin artificialtooth in which, during molding and processing with pressure and heatingfor replicating a form similar to a natural tooth while respectivelayers of the resin artificial tooth are stacked by polymerization andcuring, uniform polymerization and curing are achieved with noinfluences of the component compositions of the respective layers, thethickness of a layer structure and the like, strain generated in theresin artificial tooth is reduced to thereby inhibit defects such aslocal shrinkage, cracking, clouding and chips from being generated,molding and processing under pressure and heating conditions that causeno gas bubbles to be incorporated due to foaming can be conducted, andthe respective layers firmly adhere not to adversely affect materialproperties.

SUMMARY OF THE INVENTION

In order to solve the above problems, it has been found that, duringprocessing and molding with pressure and heating for producing ablock-shaped or disc-shaped molded product for use as a resin materialfor dental cutting and machining, the difference in heat conductivityamong respective components included in a paste-like dental curablecomposition to be polymerized and cured by heat via a mold, and thedifference in rate of polymerization in the molded product depending onthe location which is the vicinity or inside of the mold causemicro/macro-strain to be generated and cause cracks and chipping, andthat when a polymerizable monomer having a low boiling point isincluded, it is foamed in the molded product due to a rise in moldtemperature to cause gas bubbles to be incorporated, leading tocompletion of the present invention.

In detail, the rate of heat polymerization of a polymerizable monomerthat is high in heat conductivity among the components included in thedental curable composition and that starts to be rapidly polymerized byheat is decreased by addition of a chain transfer agent to thereby allowuniform heat polymerization to progress, thereby making it possible tosuppress generation of micro/macro-strain to suppress cracks andchipping. Furthermore, addition of the chain transfer material can alsosuppress foaming of the polymerizable monomer having a low boiling pointto thereby allow incorporation of gas bubbles to be suppressed, and alsoa further effect is exerted when a dental curable composition includinga filler low in heat conductivity in a large amount is molded andprocessed with pressure and heating.

In order to solve the above problems, it has been found that, when aresin artificial tooth is provided by molding and processing forreplicating a form similar to a natural tooth while respective layersare stacked by polymerization and curing, a chain transfer agent can becompounded as a component of the resin artificial tooth to therebydecrease the rate of polymerization and curing with no influences of thecomponent compositions of the layers, the thickness of a layerstructure, the locational relationship of a raw material in a mold, andthe like to provide uniform polymerization and curing, also to reduceincorporation of gas bubbles due to foaming, and furthermore to allowthe respective layers to firmly adhere, thereby resulting in reductionsin various defects caused in molding, leading to completion of thepresent invention.

Specifically, provided is a dental curable composition including (a) apolymerizable monomer and (b) a filler in a weight ratio of 10:90 to70:30, and including 0.01 to 10 parts by weight of (c) a polymerizationinitiator and 0.001 to 1 part by weight of (d) a chain transfer agentbeing a terpenoid compound based on 100 parts by weight of thepolymerizable monomer (a).

The present invention provides a dental curable composition in which,when a block-shaped or disc-shaped molded product usable as a resinmaterial for dental cutting and machining is produced while mechanicalproperties such as hardness, bending strength and compressive strengthas well as aesthetic property required for a temporary prostheticappliance, a denture base and a crown prosthetic appliance aremaintained, the dental curable composition can be molded and processedwith pressure and heating while strain generated in the molded productis reduced, no cracks and chipping occur, and no gas bubbles areincorporated due to foaming.

Micro/macro-strain in polymerization is alleviated, and therefore aresin material for dental cutting and machining, having no chipping andcracks and having any of various uniform shapes, can be produced. In thedental curable composition of the present invention, a chain transfermaterial is added to thereby allow heat polymerization to uniformlyprogress, therefore a filler can be compounded in the dental curablecomposition in a large amount, and mechanical properties such ashardness, bending strength and compressive strength as well as aestheticproperty required for a crown prosthetic appliance can be stablyexhibited at a high level.

In addition, in the dental curable composition of the present invention,even if the monofunctional polymerizable monomer having a low boilingpoint is included, the chain transfer agent is added to thereby allowpolymerization and curing to progress uniformly and slowly, resulting inno foaming, and strain can also be alleviated to thereby allow a resinmaterial for dental cutting and machining that is a uniform moldedproduct without gas bubbles, chipping, cracks, and the like to beproduced. Furthermore, the dental curable composition of the presentinvention is uniformly polymerized by addition of the chain transfermaterial, and therefore mechanical properties such as hardness, bendingstrength and compressive strength can be stably exhibited and can bemaintained at a high level as compared with material properties of atemporary prosthetic appliance or a denture base produced at a chairside or technical side.

The resin artificial tooth of the present invention, although includinga monofunctional (meth)acrylate monomer low in boiling point and high inpolymerizability, can be obtained with uniform polymerization and curingby a decrease in the rate of polymerization and curing by the effect ofthe chain transfer agent. Thus, generation of strain and incorporationof gas bubbles due to foaming in polymerization and curing can besuppressed, and therefore defects such as local shrinkage, cracking,clouding, chips and gas bubbles can be reduced. Also when the resinartificial tooth is provided by molding and processing for replicating aform similar to a natural tooth while the respective layers are stackedfor polymerization and curing, there is hardly affected by the thicknessof a layer structure and the locational relationship of a raw materialin a mold, and defects such as local shrinkage, cracking, clouding,chips and gas bubbles can be reduced.

While a composite resin layer forming the composite resin artificialtooth of the present invention includes a filler and a polymerizablemonomer having a different thermal conductivity from each other, theeffect of the chain transfer agent decreases the rate of polymerizationand curing to impart uniform polymerization and curing, and thereforemicro-strain generated at the interface between the filler and thepolymerizable monomer can be suppressed to result in no occurrence ofdefects such as local shrinkage, cracking, clouding and chips. Inaddition, an acrylic resin layer forming the composite resin artificialtooth of the present invention mainly includes a resin component high inthermal conductivity and an organic filler, therefore polymerization andcuring rapidly progress with pressure and heating, but the effect of thechain transfer agent decreases the rate of polymerization and curing toimpart uniform polymerization and curing, and therefore micro-strain ishardly generated to result in no occurrence of defects such as localshrinkage, cracking, clouding and chips. Furthermore, a local differencein thickness is caused in the same layer, but the effect of the chaintransfer agent decreases the rate of polymerization and curing tothereby impart uniform polymerization and curing with no influence ofthe thickness, resulting in no occurrence of defects such as localshrinkage, cracking, clouding and chips. In addition, the chain transferagent is compounded to thereby allow the polymerizable monomer to bepolymerized and cured at a low degree of polymerization. Therefore, whena raw material is placed on the cured layer and is polymerized and curedwith pressure and heating to be stacked, wettability therebetween can beenhanced to provide firm adhesion between the layers. As a result, notonly no defects such as local shrinkage, cracking, clouding and chipsoccur, but also excellent physical properties can be exhibited.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a simulated artificial tooth used in a non-defectivemolded product test; and

FIG. 2 is a view indicating the direction in the pressure test in aninterface adhesion state confirmation test.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present invention is described in detail.

The present invention provides a dental curable composition including(a) a polymerizable monomer and (b) a filler in a weight ratio of 10:90to 70:30, and including 0.01 to 10 parts by weight of (c) apolymerization initiator and 0.001 to 1 part by weight of (d) a chaintransfer agent being a terpenoid compound based on 100 parts by weightof the polymerizable monomer (a).

In addition, a molded body of a resin material for dental cutting andmachining produced by molding the dental curable composition of thepresent invention has a size of 1 to 350 cm³, and can have a cubicshape, for example.

The polymerizable monomer (a) that can be used in the present inventioncan be any of known monofunctional and polyfunctional polymerizablemonomers commonly used in the field of dentistry, without anylimitation. Representative examples commonly suitably used include a(meth)acrylate monomer or a (meth)acryloyl polymerizable monomer havingan acryloyl group and/or a methacryloyl group. In the present invention,the term “(meth)acrylate” or “(meth)acryloyl” inclusively refers to bothof an acryloyl group-containing polymerizable monomer and a methacryloylgroup-containing polymerizable monomer.

Specific examples of a (meth)acrylate polymerizable monomer that can beused as the polymerizable monomer (a) include the following.

Examples of a monofunctional monomer include (meth)acrylates such asmethyl(meth)acrylate, ethyl(meth)acrylate, butyl(meth)acrylate(n-butyl(meth)acrylate, i-butyl(meth)acrylate), hexyl(meth)acrylate,dicyclopentenyl(meth)acrylate, tetrahydrofurfuryl(meth)acrylate,2-hydroxyethyl(meth)acrylate, glycidyl(meth)acrylate,lauryl(meth)acrylate, cyclohexyl(meth)acrylate, benzyl(meth)acrylate,allyl(meth)acrylate, 2-ethoxyethyl(meth)acrylate, methoxy polyethyleneglycol(meth)acrylate, glycerol(meth)acrylate andisobornyl(meth)acrylate, silane compounds such asγ-(meth)acryloyloxypropyl trimethoxysilane and γ-(meth)acryloyloxypropyltriethoxysilane, and nitrogen-containing compounds such as2-(N,N-dimethylamino)ethyl(meth)acrylate, N-methylol(meth)acrylamide anddiacetone(meth)acrylamide.

Examples of an aromatic difunctional monomer include2,2-bis(4-(meth)acryloyloxyphenyl)propane,2,2-bis(4-(3-(meth)acryloyloxy-2-hydroxypropoxy)phenyl)propane,2,2-bis(4-(meth)acryloyloxyethoxyphenyl)propane,2,2-bis(4-(meth)acryloyloxydiethoxyphenyl)propane,2,2-bis(4-(meth)acryloyloxytetraethoxyphenyl)propane,2,2-bis(4-(meth)acryloyloxypentaethoxyphenyl)propane,2,2-bis(4-(meth)acryloyloxydipropoxyphenyl)propane,2(4-(meth)acryloyloxyethoxyphenyl)-2(4-(meth)acryloyloxydiethoxyphenyl)propane,2(4-(meth)acryloyloxydiethoxyphenyl)-2(4-(meth)acryloyloxytriethoxyphenyl)propane,2(4-(meth)acryloyloxydipropoxyphenyl)-2(4-(meth)acryloyloxytriethoxyphenyl)propane,2,2-bis(4-(meth)acryloyloxydipropoxyphenyl)propane and2,2-bis(4-(meth)acryloyloxyisopropoxyphenyl)propane.

Examples of an aliphatic difunctional monomer include2-hydroxy-3-acryloyloxypropyl methacrylate, hydroxypivalic acidneopentyl glycol di(meth)acrylate, ethylene glycol di(meth)acrylate,diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate,butylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate,propylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate,1,3-butanediol di(meth)acrylate, 1,4-butanediol di(meth)acrylate,1,6-hexanediol di(meth)acrylate and glycerol di(meth)acrylate.

Examples of a trifunctional monomer include trimethylolpropanetri(meth)acrylate, trimethylolethane tri(meth)acrylate,trimethylolmethane tri(meth)acrylate and pentaerythritoltri(meth)acrylate.

Examples of a tetrafunctional monomer include pentaerythritoltetra(meth)acrylate and ditrimethylolpropane tetra(meth)acrylate.

Examples of a urethane polymerizable monomer include difunctional, ortri- or higher functional urethane bond-containing di(meth)acrylatesderived from an adduct of a polymerizable monomer having a hydroxygroup, such as 2-hydroxyethyl(meth)acrylate,2-hydroxypropyl(meth)acrylate or 3-chloro-2-hydroxypropyl(meth)acrylate,and a diisocyanate compound such as methylcyclohexane diisocyanate,methylene bis(4-cyclohexylisocyanate), hexamethylene diisocyanate,trimethylhexamethylene diisocyanate, isophorone diisocyanate,diisocyanate methyl methylbenzene or 4,4-diphenylmethane diisocyanate.

An oligomer or a prepolymer having at least one polymerizable group inits molecule may be used other than such a (meth)acrylate polymerizablemonomer, without any limitation. There is no problem even if asubstituent such as a fluoro group is contained in the same molecule.

The polymerizable monomers described above can be used not only singlybut also in combinations of a plurality thereof.

When the dental curable composition of the present invention is used forproducing a molded product, is used as a resin material for dentalcutting and machining, or is used as a resin artificial tooth, amonofunctional polymerizable monomer having a boiling point of 50 to200° C. is preferable among these monofunctional monomers. Specificexamples of the monofunctional polymerizable monomer having a boilingpoint of 50 to 200° C. include methyl(meth)acrylate,ethyl(meth)acrylate, n-butyl(meth)acrylate, i-butyl(meth)acrylate,hexyl(meth)acrylate, dicyclopentenyl(meth)acrylate,2-hydroxyethyl(meth)acrylate, benzyl(meth)acrylate andphenoxyethyl(meth)acrylate, but are not limited thereto. Among thesemonofunctional polymerizable monomers, methyl(meth)acrylate,ethyl(meth)acrylate or butyl(meth)acrylate having a boiling point in therange from 70 to 170° C. is preferably used, and methyl methacrylate orethyl methacrylate having a boiling point in the range from 100 to 120°C. is more preferably used. Among these monofunctional polymerizablemonomers, methyl methacrylate is preferably used.

These monofunctional polymerizable monomers can be used not only singlybut also in combinations of a plurality thereof.

Herein, in the resin artificial tooth of the present invention, amonofunctional and/or polyfunctional polymerizable monomer other thanthe monofunctional polymerizable monomer having a boiling point of 50 to200° C. can also be used in combination as long as it has no influenceson production conditions for producing a block-shaped or disc-shapedmolded product, conditions and material properties of the moldedproduct, machining conditions in cutting and machining, and physicalproperties and molding processability of the resin artificial tooth.Representative examples commonly suitably used include a polymerizablemonomer having an acryloyl group and/or a methacryloyl group, and forexample, the above monofunctional monomer, aromatic difunctionalmonomer, aliphatic difunctional monomer, trifunctional monomer,tetrafunctional monomer and urethane polymerizable monomer can also beused in combination.

The content of the polymerizable monomer (a) that can be used in thedental curable composition of the present invention is not particularlylimited, and the dental curable composition preferably includes thepolymerizable monomer (a) and the filler (b) in a weight ratio of 10:90to 70:30, more preferably in a ratio of 10:90 to 50:50, furtherpreferably in a ratio of 20:80 to 40:60. When the weight ratio of thepolymerizable monomer (a) to the filler (b) is less than 10:90, it isdifficult to provide a composition in which the filler is uniformlydispersed, and when the weight ratio is more than 70:30, a sufficientmechanical strength cannot be achieved, and material properties aredeteriorated, for example, surface hardness is reduced. With respect tothe case where the filler (b) is a non-crosslinkable (meth)acrylatepolymer, when the weight ratio of the polymerizable monomer (a) is lessthan 10, the non-crosslinkable (meth)acrylate polymer is notsufficiently swollen and a molded body cannot be obtained, and when theweight ratio of the polymerizable monomer (a) is more than 70, a resincomponent is included in a large amount to make it difficult to controla molding technique, for example, to increase the rate of polymerizationand curing, and the following problem is found: sufficient physicalproperties are not achieved.

As the filler (b) that can be used in the present invention, a knownfiller commonly used in a dental composite material can be used. Thefiller (b) includes an inorganic filler, an organic filler and anorganic/inorganic composite filler, and these fillers can be used notonly singly but also in combinations of a plurality thereof regardlessof the types of the fillers.

Specific examples of the inorganic filler include silica, aluminumsilicate, alumina, titania, zirconia, various glasses (includingfluoride glass, borosilicate glass, soda glass, barium glass, bariumaluminum silica glass, glass including strontium or zirconium, glassceramics, fluoroaluminosilicate glass, and synthetic glass by a sol-gelmethod), Aerosil (registered trademark), calcium fluoride, strontiumfluoride, calcium carbonate, kaolin, clay, mica, aluminum sulfate,calcium sulfate, barium sulfate, titanium oxide, calcium phosphate,hydroxyapatite, calcium hydroxide, strontium hydroxide and zeolite. Suchan inorganic filler may also be used as an aggregate, and examples ofthe aggregate include a silica-zirconia composite oxide aggregateobtained by mixing silica sol and zirconia sol and subjecting themixture to spray drying and a heat treatment.

Examples of the organic filler include elastomers such as polyvinylacetate, polyvinyl alcohol and a styrene-butadiene rubber,non-crosslinkable (meth)acrylate polymers each being a homopolymer of amonofunctional (meth)acrylate polymerizable monomer, such as polymethylmethacrylate (PMMA), polyethyl methacrylate, polypropyl methacrylate andpolybutyl methacrylate, crosslinkable (meth)acrylate polymers obtainedby copolymerizing a monofunctional (meth)acrylate polymerizable monomerwith a polymerizable monomer having two or more functional groups, andpolyvinyl acetate, polyethylene glycol, polypropylene glycol andpolyvinyl alcohol, but are not limited thereto.

In addition, examples of the organic/inorganic composite filler includeone obtained by covering the surface of a filler with a polymerizablemonomer by polymerization, one obtained by mixing a filler and apolymerization monomer and polymerizing the monomer, and thereaftergrinding the resultant to a proper particle size, or one obtained bydispersing a filler in a polymerizable monomer in advance for emulsionpolymerization or suspension polymerization, but are not limited theretoat all.

As such a filler, a filler having any shape such as a spherical shape, aneedle shape, a plate shape, a crushed shape or a scale shape can beused. The average particle size of the filler is different depending onthe type of the filler, and in the case of the inorganic filler, anyfiller can be used as long as it has an average particle size in therange from 0.05 to 200 μm, preferably in the range from 0.5 to 100 μm,more preferably in the range from 1 to 20 μm. In the case of theorganic/inorganic composite type filler, any filler can be used as longas it has an average particle size in the range from 0.05 to 150 μm,preferably in the range from 0.5 to 100 μm, more preferably in the rangefrom 1 to 20 μm. Furthermore, in the case of the organic filler, theaverage particle size is not particularly limited, and any filler havingan average particle size in any range can be used. Herein, theinformation on the average particle size can be examined by a laserdiffraction type particle size measurement machine. When the filler (b)is an aggregate, the above average particle size corresponds to theaverage particle size of the aggregate. The average particle size of thefiller is preferably in the range from 0.5 to 100 μm, more preferably inthe range from 1 to 20 μm. Herein, the information on the averageparticle size and the variation coefficient of the particle size, andthe like can be examined by a laser diffraction type particle sizemeasurement machine, and when the filler (b) is an aggregate, the aboveaverage particle size corresponds to the average particle size of theaggregate. When the average particle size is less than 0.5 μm, thedental curable composition is sticky and gas bubbles are easilyincorporated. When the average particle size is more than 100 μm, thefiller (b) is easily precipitated in the composition and may not beuniformly dispersed.

The surface of the filler may also be multi-functionalized by a surfacetreatment method using a surface treatment agent, and the fillersubjected to a surface treatment can be used without any limitation.Specific examples of the surface treatment agent for use inmulti-functionalizing the surface of the filler include a surfactant, afatty acid, an organic acid, an inorganic acid, various couplingmaterials (a titanate coupling agent, an aluminate coupling agent and asilane coupling agent), and a metal alkoxide compound. Specific examplesof the surface treatment method include a method of spraying the surfacetreatment agent from above in the state of allowing the filler to flow,a method of dispersing the filler in a solution including the surfacetreatment agent, and a method of applying several surface treatmentagents on the surface of the filler by a multilayer treatment. Thesurface treatment agent and the surface treatment method, however, arenot limited thereto. Moreover, each of the surface treatment agent andthe surface treatment method can be used singly or in combinationcompositely.

The content of the filler (b) that can be used in the present inventionis not particularly limited, and the content thereof in the dentalcurable composition is preferably 30 to 90 parts by weight, morepreferably 50 to 90 parts by weight. If the content of the filler (b) isless than 30 parts by weight, a sufficient mechanical strength cannot beachieved, and if the content is more than 90 parts by weight, it isdifficult to provide a dental curable composition in which the filler isuniformly dispersed.

In addition, the content of the filler (b) that can be used in acomposite resin layer forming the composite resin artificial tooth ofthe present invention is not particularly limited, and the contentthereof in the composite resin layer is preferably in the range from 30to 90 parts by weight, more preferably in the range from 30 to 60 partsby weight. If the content of the filler is less than 30 parts by weight,material properties are deteriorated, for example, surface hardness isreduced, and on the other hand, if the content is more than 90 parts byweight, a resin component is contained in a small amount to deterioratewettability between respective layers and not to impart sufficientadhesion, and therefore the problem of deterioration in materialproperties is caused.

Such a filler may be subjected to a surface treatment with a knowntitanate coupling agent, aluminate coupling agent or silane couplingagent without any problem. Examples of the silane coupling agent includeγ-methacryloxypropyl trimethoxysilane and γ-methacryloxypropyltriethoxysilane. Preferably, γ-methacryloxypropyl trimethoxysilane isused. The aggregate and the filler may be subjected to a surfacetreatment with the same coupling agent or a different coupling agent.

In the dental curable composition of the present invention, when thepolymerizable monomer (a) is the monofunctional polymerizable monomerhaving a boiling point of 50 to 200° C., a non-crosslinkable(meth)acrylate polymer is preferably used as the filler (b). Thenon-crosslinkable (meth)acrylate polymer is not particularly limited aslong as it is swollen by the monofunctional polymerizable monomer, and apolymer obtained by homopolymerization of a (meth)acrylate polymerizablemonomer, a polymer obtained by copolymerization of a plurality of such(meth)acrylate polymerizable monomers, a polymer obtained bycopolymerization of the (meth)acrylate polymerizable monomer withanother polymerizable monomer, or the like can be used therefor withoutany limitation. Specific examples of the non-crosslinkable(meth)acrylate polymer include homopolymers such aspolymethyl(meth)acrylate, polyethyl(meth)acrylate,polypropyl(meth)acrylate, polyisopropyl(meth)acrylate,polyisobutyl(meth)acrylate and polybutyl(meth)acrylate, and copolymersof two or more among methyl(meth)acrylate, ethyl(meth)acrylate, propyl(meth)acrylate, isopropyl(meth)acrylate, isobutyl(meth)acrylate andbutyl(meth)acrylate, but are not limited thereto. Thesenon-crosslinkable (meth)acrylate polymers can be used not only singlybut also in combinations of a plurality thereof. Among thesenon-crosslinkable (meth)acrylate polymers, polymethyl methacrylate,polyethyl methacrylate, or a copolymer of methyl methacrylate with ethylmethacrylate is preferably used. Polymethyl methacrylate is mostpreferably used.

The method for providing such a non-crosslinkable (meth)acrylate polymerby polymerization is not limited at all, and there is no problem even ifthe non-crosslinkable (meth)acrylate polymer is obtained by anypolymerization method such as emulsion polymerization or suspensionpolymerization. The non-crosslinkable (meth)acrylate polymer can be usedwithout any limitation, even if having any shape such as a sphericalshape, a crushed shape or a hollow shape, but preferably a sphericalshape. The non-crosslinkable (meth)acrylate polymer can be used withoutany limitation as long as the average particle size (50%) thereof is inthe range from 1 to 300 μm, preferably in the range from 1 to 200 μm,further preferably in the range from 5 to 150 μm. The non-crosslinkable(meth)acrylate polymer can be used without any limitation as long as theweight average molecular weight thereof is in the range from 10000 to2000000, preferably in the range from 50000 to 1500000, furtherpreferably in the range from 100000 to 1500000.

In addition, any one can be used without any limitation, in which thesurface of an organic filler, an inorganic filler, an organic/inorganiccomposite filler, an organic/inorganic compound, an organic/inorganicpigment or the like is subjected to secondary processing such as asurface modification treatment or a composite-forming treatment in whichthe surface is covered with the non-crosslinkable (meth)acrylatepolymer.

The non-crosslinkable (meth)acrylate polymer for use in the dentalcurable composition of the present invention can be used without anylimitation as long as the content thereof is in the range from 30 to 90parts by weight, preferably in the range from 40 to 90 parts by weight,more preferably in the range from 50 to 90 parts by weight, furtherpreferably in the range from 50 to 80 parts by weight, most preferablyin the range from 60 to 80 parts by weight.

If the content of the non-crosslinkable (meth)acrylate polymer is lessthan 30 parts by weight, there is the problem of an excess of themonofunctional polymerizable monomer having a boiling point of 50 to200° C. not to allow uniform swelling to occur. On the other hand, ifthe content is more than 90% by weight, there is the problem of anexcess of the non-crosslinkable (meth)acrylate polymer not to allowuniform curing to occur, resulting in an ununiform product in molding.With respect to the case where the non-crosslinkable (meth)acrylatepolymer is used for the resin artificial tooth, if the content of thenon-crosslinkable (meth)acrylate polymer is less than 30 parts byweight, an excess of the monofunctional polymerizable monomer is presentto increase the rate of polymerization and curing to adversely affectmoldability, and sufficient physical properties cannot be achieved. Onthe other hand, if the content is more than 90 parts by weight, themonofunctional polymerizable monomer cannot allow an excessive amount ofthe non-crosslinkable (meth)acrylate polymer to be uniformly swollen,and the problem of moldability is caused.

Herein, a filler other than the non-crosslinkable (meth)acrylate polymercan be used as the filler (b) as long as it has no influences onphysical properties, aesthetic property and moldability of the resinartificial tooth of the present invention. As such a filler, an organiccomponent, an inorganic component, and a mixture or composite thereofcan be used without any limitation as long as these do not allow themonofunctional (meth)acrylate polymerizable monomer to be swollen.

Specific examples of the filler other than the non-crosslinkable(meth)acrylate polymer include inorganic fillers including metalhydroxides such as aluminum hydroxide, calcium hydroxide and magnesiumhydroxide, carbonates such as calcium carbonate and strontium carbonate,metal oxides such as aluminum oxide, metal fluorides such as bariumfluoride, calcium fluoride and strontium fluoride, and talc, kaolin,clay, mica, hydroxyapatite, silica, quartz, and various glasses (glassesof sodium, heavy metals such as strontium, barium and lanthanum and/orfluorine-containing fluoroaluminosilicate, borosilicate, aluminoborate,fluoroalumino borosilicate, and the like), organic fillers includingelastomers such as polyvinyl acetate, polyvinyl alcohol and astyrene-butadiene rubber, and a crosslinkable (meth)acrylate polymerobtained by copolymerization of a monofunctional (meth)acrylatepolymerizable monomer with a polymerizable monomer having two or morefunctional groups, and organic/inorganic composite type fillers such asone in which the surface of an inorganic filler is covered bypolymerization of a polymerizable monomer, one obtained by mixing aninorganic filler and a polymerization monomer and polymerizing themonomer, and thereafter grinding the resultant to a proper particlesize, and one obtained by dispersing a filler in a polymerizable monomerin advance for emulsion polymerization or suspension polymerization, butare not limited thereto. These fillers can be used not only singly butalso in combinations of a plurality thereof.

As the filler other than the non-crosslinkable (meth)acrylate polymer, afiller having any shape such as a spherical shape, a needle shape, aplate shape, a crushed shape or a scale shape can be used. The filler isnot particularly limited as long as the average particle size (50%)thereof is in the range from 1 to 200 preferably in the range from 5 to100 μm, further preferably in the range from 10 to 80 μm.

The surface of the filler other than the non-crosslinkable(meth)acrylate polymer may be further multi-functionalized by a surfacetreatment method using a surface treatment agent or the like, and such afiller subjected to a surface treatment can also be used without anylimitation. Specific examples of the surface treatment agent for use inmulti-functionalizing the surface of the filler include a surfactant, afatty acid, an organic acid, an inorganic acid, various couplingmaterials and a metal alkoxide compound. In addition, specific examplesof the surface treatment method include a method of spraying the surfacetreatment agent from above in the state of allowing the filler to flow,a method of dispersing the filler in a solution including the surfacetreatment agent, and a method of applying several surface treatmentagents on the surface of the filler by a multilayer treatment. Thesurface treatment agent and the surface treatment method, however, arenot limited thereto. Moreover, each of the surface treatment agent andthe surface treatment method can be used singly or in combinationcompositely.

The polymerization initiator (c) that can be used in the presentinvention is not particularly limited, and a known polymerizationinitiator, for example, a radical generator is used without anylimitation. The polymerization initiator is roughly classified into aninitiator that is mixed immediately before use to thereby initiatepolymerization (chemical polymerization initiator), an initiator thatinitiates polymerization by heating or warming (heat polymerizationinitiator), and an initiator that initiates polymerization byirradiation with light (photo-polymerization initiator), and anypolymerization initiator thereof can be used in the present inventionwithout any limitation. These polymerization initiators can be used notonly singly but also in combinations of a plurality thereof, regardlessof the polymerization manner or the polymerization method. Furthermore,these polymerization initiators can be used without any problem, even ifbeing subjected to a secondary treatment such as encapsulation in amicrocapsule for the purposes of realizing stabilization ofpolymerization or delaying of polymerization. Among these polymerizationinitiators, a heat polymerization initiator is preferably used.

For the heat polymerization initiator, specifically, for example,organic peroxides such as benzoyl peroxide, p-chlorobenzoyl peroxide,2,4-dichlorobenzoyl peroxide, acetyl peroxide, lauroyl peroxide,tert-butyl peroxide, cumene hydroperoxide, 2,5-dimethylhexane,2,5-dihydroperoxide, methyl ethyl ketone peroxide andtert-butylperoxybenzoate, and azo compounds such asazobisisobutyronitrile, azobis(methyl isobutyrate) or azobiscyanovalericacid are suitably used. Among them, organic peroxides are preferablyused, more preferably benzoyl peroxide.

These polymerization initiators can be used without any limitation, evenif subjected to secondary processing in order to control polymerizationproperties or ensure stability.

For the chemical polymerization initiator, a redox type polymerizationinitiation system of organic peroxide/amine compound, organicperoxide/amine compound/sulfinate, organic peroxide/aminecompound/barbituric acid or barbituric acid derivative, or organicperoxide/amine compound/borate compound, an organometal polymerizationinitiator system in which a reaction with oxygen or water allowspolymerization to be initiated, or the like is used. Sulfinates andborate compounds can be used because of being capable of reacting with apolymerizable monomer having an acidic group to thereby initiatepolymerization.

Specific examples of the chemical polymerization initiator are shownbelow, but are not limited to the following.

Specific examples of the organic peroxide include benzoyl peroxide,p-chlorobenzoyl peroxide, 2,4-dichlorobenzoyl peroxide, acetyl peroxide,lauroyl peroxide, tert-butyl peroxide, cumene hydroperoxide,2,5-dimethyl-2,5-di(benzoylperoxy)hexane, 2,5-dihydroperoxide, methylethyl ketone peroxide and tert-butylperoxybenzoate.

Specific examples of the amine compound preferably include a secondaryor tertiary amine in which an amine group is bound to an aryl group, andspecific examples include p-N,N-dimethyl-toluidine, N,N-dimethylaniline,N-β-hydroxyethyl-aniline, N,N-di(β-hydroxyethyl)-aniline,p-N,N-di(β-hydroxyethyl)-toluidine, N-methyl-aniline andp-N-methyl-toluidine.

Specific examples of the sulfonates include sodium benzenesulfinate,lithium benzenesulfinate and sodium p-toluenesulfinate.

Specific examples of the barbituric acid and derivatives thereof includebarbituric acid, 1,3-dimethylbarbituric acid, 1,3-diphenylbarbituricacid, 1,5-dimethylbarbituric acid, 5-butylbarbituric acid,5-ethylbarbituric acid, 5-isopropylbarbituric acid,5-cyclohexylbarbituric acid, 1,3,5-trimethylbarbituric acid,1,3-dimethyl-5-ethylbarbituric acid, 1,3-dimethyl-n-butylbarbituricacid, 1,3-dimethyl-5-isobutylbarbituric acid,1,3-dimethyl-5-tert-butylbarbituric acid,1,3-dimethyl-5-cyclopentylbarbituric acid,1,3-dimethyl-5-cyclohexylbarbituric acid,1,3-dimethyl-5-phenylbarbituric acid, 1-cyclohexyl-5-ethylbarbituricacid, 1-benzyl-5-phenylbarbituric acid and thiobarbituric acids, as wellas salts thereof (particularly preferably alkali metal or alkaline-earthmetal salts), for example, sodium 5-butylbarbiturate, sodium1,3,5-trimethylbarbiturate, calcium 1,3,5-trimethylbarbiturate andsodium 1-cyclohexyl-5-ethylbarbiturate.

Specific examples of the borate compound include sodium salts, lithiumsalts, potassium salts, magnesium salts, tetrabutylammonium salts andtetramethylammonium salts of trialkylphenylboron andtrialkyl(p-chlorophenyl)boron (an alkyl group is a n-butyl group, an-octyl group, a n-dodecyl group or the like).

Furthermore, specific examples of the organometal polymerizationinitiator include organic boron compounds such as triphenylborane,tributylborane and tributylborane partial oxide.

Specific examples of perborate include sodium perborate, potassiumperborate and ammonium perborate, specific examples of permanganateinclude ammonium permanganate, potassium permanganate and sodiumpermanganate, and furthermore specific examples of persulfate includeammonium persulfate, potassium persulfate and sodium persulfate. For theheat polymerization initiator by heating or warming, azo compounds suchas azobisisobutyronitrile, azobis(methyl isobutyrate) andazobiscyanovaleric acid, other than the above organic peroxides, aresuitably used.

For the photo-polymerization initiator, one made of a photosensitizer,for example, photosensitizer/photopolymerization promoter is used.Specific examples of the photo-polymerization initiator are shown below,but are not limited to the following.

Specific examples of the photosensitizer include α-diketones such asbenzyl, camphor quinone, α-naphthyl, acetonaphthene,p,p′-dimethoxybenzyl, p,p′-dichlorobenzylacetyl, pentanedione,1,2-phenanthrenequinone, 1,4-phenanthrenequinone,3,4-phenanthrenequinone, 9,10-phenanthrenequinone and naphthoquinone,benzoin alkyl ethers such as benzoin, benzoin methyl ether and benzoinethyl ether, thioxanthones such as thioxanthone, 2-chlorothioxanthone,2-methylthioxanthone, 2-isopropylthioxanthone, 2-methoxythioxanthone,2-hydroxythioxanthone, 2,4-diethylthioxanthone and2,4-diisopropylthioxanthone, benzophenones such as benzophenone,p-chlorobenzophenone and p-methoxybenzophenone, acylphosphine oxidessuch as 2,4,6-trimethylbenzoyl diphenylphosphine oxide andbis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide,α-aminoacetophenones such as2-benzyl-dimethylamino-1-(4-morpholinophenyl)-butanone-1,2-benzyl-diethylamino-1-(4-morpholinophenyl)-propanone-1,ketals such as benzyl dimethyl ketal, benzyl diethyl ketal andbenzyl(2-methoxyethyl ketal), and titanocenes such asbis(cyclopentadienyl)-bis[2,6-difluoro-3-(1-pyrrolyl)phenyl]-titanium,bis(cyclopentadienyl)-bis(pentanefluorophenyl)-titanium andbis(cyclopentadienyl)-bis(2,3,5,6-tetrafluoro-4-disiloxyphenyl)-titanium.

Specific examples of the photopolymerization promoter include tertiaryamines such as N,N-dimethylaniline, N,N-diethylaniline,N,N-di-n-butylaniline, N,N-dibenzylaniline, p-N,N-dimethyl-toluidine,m-N,N-dimethyl-toluidine, p-N,N-diethyl-toluidine,p-bromo-N,N-dimethylaniline, m-chloro-N,N-dimethylaniline,p-dimethylaminobenzaldehyde, p-dimethylaminoacetophenone,p-dimethylaminobenzoic acid, p-dimethylaminobenzoic acid ethyl ester,p-dimethylaminobenzoic acid amino ester, N,N-dimethylanthranilic acidmethyl ester, N,N-dihydroxyethylaniline, p-N,N-dihydroxyethyl-toluidine,p-dimethylaminophenyl alcohol, p-dimethylaminostyrene,N,N-dimethyl-3,5-xylidine, 4-dimethylaminopyridine,N,N-dimethyl-α-naphthylamine, N,N-dimethyl-β-naphthylamine,tributylamine, tripropylamine, triethylamine, N-methyldiethanolamine,N-ethyldiethanolamine, N,N-dimethylhexylamine, N,N-dimethyldodecylamine,N,N-dimethylstearylamine, N,N-dimethylaminoethyl methacrylate,N,N-diethylaminoethyl methacrylate and 2,2′-(n-butylimino)diethanol,secondary amines such as N-phenylglycine, barbituric acids such as5-butylbarbituric acid and 1-benzyl-5-phenylbarbituric acid, tincompounds such as dibutyl tin diacetate, dibutyl tin dilaurate, dioctyltin dilaurate, dioctyl tin diversatate, a dioctyl tin bis(mercaptoaceticacid isooctyl ester) salt and tetramethyl-1,3-diacetoxydistannoxane,aldehyde compounds such as laurylaldehyde and terephthalaldehyde, andsulfur-containing compounds such as dodecylmercaptan,2-mercaptobenzoxazole, 1-decanethiol and thiosalicylic acid.

In order to enhance photopolymerization promotion performances, it iseffective to add, in addition to the above photopolymerization promoter,oxycarboxylic acids such as citric acid, malic acid, tartaric acid,glycolic acid, gluconic acid, α-oxyisobutyric acid, 2-hydroxypropanoicacid, 3-hydroxypropanoic acid, 3 hydroxybutanoic acid, 4-hydroxybutanoicacid and dimethylolpropionic acid.

These polymerization initiators can be used not only singly but also incombinations of two or more, regardless of the polymerization manner orthe polymerization method. In addition, these polymerization initiatorshave no problem even if subjected to a secondary treatment such asencapsulation in a microcapsule, if necessary.

Such a polymerization initiator is used in production of thenon-crosslinkable (meth)acrylate polymer as the filler (b), and thepolymerization initiator may remain in the non-crosslinkable(meth)acrylate polymer produced. Therefore, when a non-crosslinkable(meth)acrylate polymer in which the polymerization initiator remains isused for the resin artificial tooth of the present invention, it can beused instead of or as part of the polymerization initiator (c) withoutany problem.

The content of the polymerization initiator (c) for use in the curabledental composition of the present invention can be appropriatelyselected depending on the application, and the method for producing ablock as the resin material for dental cutting and machining, and ispreferably in the range from 0.01 to 10 parts by weight, more preferablyin the range from 0.1 to 5 parts by weight, further preferably in therange from 0.1 to 2 parts by weight based on 100 parts by weight of thepolymerizable monomer (a). If the amount of the polymerization initiator(c) to be compounded is less than 0.01 parts by weight, polymerizationdoes not sufficiently progress to deteriorate mechanical strength, andif the amount is more than 10 parts by weight, the polymerizationinitiator (c) may be precipitated from the composition. When thepolymerizable monomer (a) is the monofunctional polymerizable monomerhaving a boiling point of 50 to 200° C. and the filler (b) is thenon-crosslinkable (meth)acrylate polymer, a content of thepolymerization initiator of 0.1 parts by weight or more allowspolymerization and curing to be uniform, and can inhibit sufficientphysical properties from not being achieved due to the presence of theremaining unreacted monomer, polymerization defect, or the like. If thecontent is 5 parts by weight or less, the following problem issuppressed: polymerization and curing progress quickly not to enable tocontrol the rate of polymerization of the monofunctional polymerizablemonomer and not to take a margin for operation in production of a disc,resulting in rapid curing.

When the polymerization initiator (c) is used in the composite resinlayer forming the composite resin artificial tooth, it can be usedwithout particular limitation as long as the content thereof is in therange from 0.01 to 10 parts by weight, preferably in the range from 0.05to 5 parts by weight, more preferably in the range from 0.1 to 5 partsby weight based on 100 parts by weight of the polymerizable monomer (a).If the amount of the polymerization initiator (c) to be compounded isless than 0.01 parts by weight, polymerization does not sufficientlyprogress to deteriorate mechanical properties, and if the amount is morethan 10 parts by weight, polymerization and curing rapidly occur andtherefore defects such as local shrinkage, cracking, clouding and chipscan be caused.

Furthermore, when the polymerization initiator (c) is used for the resinartificial tooth in which the polymerizable monomer (a) is themonofunctional polymerizable monomer having a boiling point of 50 to200° C. and the filler (b) is the non-crosslinkable (meth)acrylatepolymer, the content thereof is preferably in the range from 0.1 to 5parts by weight, more preferably in the range from 0.1 to 2 parts byweight based on 100 parts by weight of the polymerizable monomer (a). Ifthe content of the polymerization initiator is less than 0.1 parts byweight, polymerization and curing do not occur uniformly, and sufficientphysical properties are not achieved due to the presence of theremaining unreacted monomer, polymerization defect, or the like. If thecontent is more than 5 parts by weight, the following problem is caused:polymerization and curing progress too quickly to enable to control therate of polymerization of the monofunctional polymerizable monomer foruniform molding, thereby deteriorating physical properties to result inrapid curing.

For the chain transfer agent (d) for use in the curable dentalcomposition of the present invention, a known compound can be usedwithout any limitation. Specific examples include mercaptan compoundssuch as n-butylmercaptan and n-octylmercaptan, terpenoid compounds suchas limonene, myrcene, α-terpinene, β-terpinene, γ-terpinene,terpinolene, β-pinene and α-pinene, and an α-methylstyrene dimer. Amongthese chain transfer materials, terpenoid compounds are particularlypreferable. Specifically, α-terpinene, β-terpinene and γ-terpinene areparticularly preferable. These chain transfer agents can be used notonly singly but also in combinations of two or more. In particular,γ-terpinene is most preferable. The amount of such a chain transferagent to be added is preferably 0.001 to 1 part by weight, particularlypreferably 0.1 parts by weight or more and 0.5 parts by weight or lessbased on 100 parts by weight of the polymerizable monomer (a). If theamount of the chain transfer agent (d) to be compounded is less than0.001 parts by weight, strain of the inside, caused in polymerization ofthe dental curable composition, cannot be sufficiently suppressed. Ifthe amount is more than 1 part by weight, the amount of the unreactedpolymerizable monomer remaining in the composition after curing may beincreased to deteriorate mechanical strength.

When the polymerizable monomer (a) is the monofunctional polymerizablemonomer having a boiling point of 50 to 200° C. and the filler (b) isthe non-crosslinkable (meth)acrylate polymer, the amount of the chaintransfer agent to be added is preferably 0.001 to 1 part by weight,particularly preferably 0.1 to 0.5 parts by weight based on 100 parts byweight of the polymerizable monomer (a). If the content of the chaintransfer agent is less than 0.001 parts by weight, the rate ofpolymerization and curing cannot be decreased, strain is generated inmolding, and defects such as local shrinkage, cracking, clouding andchips, and incorporation of gas bubbles due to foaming cannot besuppressed. On the other hand, if the content is 1 part by weight ormore, polymerization and curing do not progress and sufficient physicalproperties cannot be achieved.

When the chain transfer agent (d) is used in the composite resin layerforming the composite resin artificial tooth of the present invention,the content thereof is preferably in the range from 0.001 to 1 part byweight, more preferably in the range from 0.1 to 0.5 parts by weightbased on 100 parts by weight of the polymerizable monomer (a). If thecontent of the chain transfer agent (d) is less than 0.001 parts byweight, rapid polymerization and curing can occur in molding withheating and pressure to cause defects such as local shrinkage, cracking,clouding and chips to be generated. On the other hand, if the content ismore than 1 part by weight, the polymerization and curing reaction maybe suppressed to thereby cause the proportion of the unreactedpolymerizable monomer present to be higher, resulting in deteriorationin material properties.

When the chain transfer agent is used in the resin artificial tooth inwhich the polymerizable monomer (a) is the monofunctional polymerizablemonomer having a boiling point of 50 to 200° C. and the filler (b) isthe non-crosslinkable (meth)acrylate polymer, the content thereof is inthe range from 0.001 to 1 part by weight, preferably 0.001 to 3 parts byweight, particularly preferably 0.1 to 0.5 parts by weight based on 100parts by weight of the polymerizable monomer (a). If the content of thechain transfer agent is less than 0.001 parts by weight, the rate ofpolymerization and curing cannot be decreased, strain is generated inmolding, and defects such as local shrinkage, cracking, clouding andchips, and incorporation of gas bubbles due to foaming cannot besuppressed. On the other hand, if the content is 3 parts by weight ormore, polymerization and curing do not progress and sufficient physicalproperties cannot be achieved.

To the dental curable composition of the present invention, a componentsuch as an excipient typified by fumed silica, an ultraviolet absorbersuch as 2-hydroxy-4-methylbenzophenone, a polymerization inhibitor suchas hydroquinone, hydroquinone monomethyl ether or2,5-ditert-butyl-4-methylphenol, a discoloration inhibitor, anantibacterial material, a coloring pigment, or other conventionallyknown additive can be if necessary added arbitrarily, in addition to theabove components (a) to (d).

In the composite resin artificial tooth of the present invention, atleast one layer including a base layer that can chemically adhere to adenture base is an acrylic resin layer. For (e) a monofunctional(meth)acrylate polymerizable monomer that can be used in the acrylicresin layer forming the composite resin artificial tooth of the presentinvention, any monomer among known monofunctional (meth)acrylatepolymerizable monomers having an acryloyl group and/or a methacryloylgroup, commonly used in the field of dentistry, can be used without anylimitation. In the present invention, the term “monofunctional(meth)acrylate polymerizable monomer” inclusively refers to both of anacryloyl group-containing polymerizable monomer and a methacryloylgroup-containing polymerizable monomer.

Specific examples of the monofunctional (meth)acrylate polymerizablemonomer (e) include the following. Examples of the monofunctional(meth)acrylate polymerizable monomer include (meth)acrylates such asmethyl(meth)acrylate, ethyl(meth)acrylate, butyl(meth)acrylate,hexyl(meth)acrylate, glycidyl(meth)acrylate, lauryl(meth)acrylate,cyclohexyl(meth)acrylate, benzyl(meth)acrylate, allyl(meth)acrylate,2-ethoxyethyl(meth)acrylate, glycerol(meth)acrylate andisobornyl(meth)acrylate, silane compounds such asγ-(meth)acryloyloxypropyl trimethoxysilane and γ-(meth)acryloyloxypropyltriethoxysilane, and nitrogen-containing compounds such as2-(N,N-dimethylamino)ethyl(meth)acrylate and N-methylol(meth)acrylamide.These monofunctional (meth)acrylate polymerizable monomers can be usednot only singly but also in combinations of a plurality thereof.

The content of the monofunctional (meth)acrylate polymerizable monomer(e) that can be used in the acrylic resin layer forming the compositeresin artificial tooth of the present invention is not particularlylimited, and in particular preferably in the range from 10 to 70 partsby weight, more preferably in the range from 10 to 50 parts by weight,further preferably in the range from 20 to 40 parts by weight. If thecontent of the monofunctional (meth)acrylate polymerizable monomer isless than 10 parts by weight, adhesiveness to a denture base isdeteriorated, and on the other hand, if the content is more than 70parts by weight, the following problem is caused: polymerizationshrinkage of a resin component is increased to thereby deterioratemoldability, making it impossible to achieve stable dimensionalstability, for example.

(f) A non-crosslinkable (meth)acrylate polymer that can be used in theacrylic resin layer forming the composite resin artificial tooth of thepresent invention is not particularly limited as long as it is swollenby a monofunctional (meth)acrylate polymerizable monomer, and a polymerobtained by homopolymerizing the (meth)acrylate polymerizable monomer, apolymer obtained by copolymerizing a plurality of such (meth)acrylatepolymerizable monomers, a polymer obtained by copolymerizing the(meth)acrylate polymerizable monomer with another monofunctionalpolymerizable monomer, or the like can be used without any limitation.Specific examples of the (meth)acrylate polymer include homopolymerssuch as polymethyl(meth)acrylate, polyethyl(meth)acrylate,polypropyl(meth)acrylate, polyisopropyl(meth)acrylate,polyisobutyl(meth)acrylate and polybutyl(meth)acrylate, and copolymersof a combination of two or more among methyl(meth)acrylate,ethyl(meth)acrylate, propyl(meth)acrylate, isopropyl(meth)acrylate,isobutyl(meth)acrylate and butyl(meth)acrylate, but are not limitedthereto. These non-crosslinkable (meth)acrylate polymers can be used notonly singly but also in combinations of a plurality thereof. Among thesenon-crosslinkable (meth)acrylate polymers, polymethyl methacrylate,polyethyl methacrylate, or a copolymer of methyl methacrylate with ethylmethacrylate is preferably used.

Such a non-crosslinkable (meth)acrylate polymer is not limited at all interms of the polymerization method, and can be produced by anypolymerization method such as emulsion polymerization or suspensionpolymerization without any problem. The non-crosslinkable (meth)acrylatepolymer can be used without any limitation, even if having any shapesuch as a spherical shape, a crushed shape or a hollow shape, butpreferably a spherical shape.

The non-crosslinkable (meth)acrylate polymer can be used without anylimitation as long as the average particle size (50 parts) thereof is inthe range from 1 to 300 μm, preferably in the range from 1 to 200 μm,further preferably in the range from 5 to 150 μm. The non-crosslinkable(meth)acrylate polymer can be used without any limitation as long as theweight average molecular weight thereof is in the range from 10000 to2000000, preferably in the range from 50000 to 1500000, furtherpreferably in the range from 100000 to 1500000.

In addition, any one can be used without any limitation, in which thesurface of an organic filler, an inorganic filler, an organic/inorganiccomposite type filler, an organic/inorganic compound, anorganic/inorganic pigment or the like is subjected to secondaryprocessing such as a surface modification treatment or acomposite-forming treatment in which the surface is covered with thenon-crosslinkable (meth)acrylate polymer.

The non-crosslinkable (meth)acrylate polymer (f) that can be used in theacrylic resin layer forming the composite resin artificial tooth of thepresent invention can be used without any limitation as long as thecontent thereof is in the range from 30 to 90 parts by weight,preferably in the range from 50 to 90 parts by weight, furtherpreferably in the range from 60 to 80 parts by weight.

If the content of the non-crosslinkable (meth)acrylate polymer is lessthan 30 parts by weight, adhesiveness to a denture base is deteriorated,and on the other hand, if the content is more than 90 parts by weight,the following problem is caused: polymerization shrinkage of a resincomponent is increased to thereby deteriorate moldability, making itimpossible to achieve stable dimensional stability, for example.

To the composite resin layer or the acrylic resin layer forming thecomposite resin artificial tooth of the present invention, a componentsuch as an excipient typified by fumed silica, an ultraviolet absorbersuch as 2-hydroxy-4-methylbenzophenone, a polymerization inhibitor suchas hydroquinone, hydroquinone monomethyl ether or2,5-ditert-butyl-4-methylphenol, a discoloration inhibitor, anantibacterial material, a coloring pigment, or other conventionallyknown additive can be if necessary added arbitrarily, in addition to theabove components (a) to (d).

The method for producing a resin for dental cutting and machining, usingthe dental curable composition of the present invention, is not limitedat all. Examples include a method of packing in a mold the dentalcurable composition, to which the heat polymerization initiator isadded, for production with pressure and heating, and a method of packingin a mold the dental curable composition, to which thephoto-polymerization initiator and the heat polymerization initiator areadded, and subjecting a surface layer portion to polymerization byirradiation with light, before heating, for sufficient curing to theinside.

The size and the shape of the resin material for dental cutting andmachining, produced using the dental curable composition of the presentinvention, are not limited at all. Examples include a prism shape of12×14×18 mm, and a disc shape having 10 to 30 mm in thickness×98 mm indiameter.

The method for producing the composite resin artificial tooth of thepresent invention is not limited at all. Examples include a compressionmolding method of packing in a mold a rice cake-like raw material, inwhich a paste or powder material is admixed with a liquid material, forpressurizing and heating, and an injection molding method of injectingthe raw material into a mold at a constant pressure, but are not limitedthereto. In particular, a production method of sequentially subjectingeach of the composite resin layer or the acrylic resin layer singly topolymerization and curing with heating and pressure, for stacking ispreferable.

When the composite resin artificial tooth of the present invention has amonolayer or multilayer structure having the composite resin layer,chemical adhesion with a denture base cannot be expected, and thereforean adhesive primer is used or a maintaining hole is formed for providingmechanical fitting without any limitation. When the composite resinartificial tooth of the present invention is configured from at leastone layer as the composite resin layer and at least one layer as theacrylic resin layer, including a base layer that can chemically adhereto a denture base, it can have a multilayer structure without anylimitation in the number of layers and the types thereof. The shape andthe size thereof are not limited, and various shapes and sizes can beadopted without any problem.

Examples Dental Curable Composition

Hereinafter, Examples of the dental curable composition of the presentinvention including (a) a polymerizable monomer and (b) a filler in aweight ratio of 10:90 to 70:30, and including 0.01 to 10 parts by weightof (c) a polymerization initiator and 0.001 to 1 part by weight of (d) achain transfer agent being a terpenoid compound based on 100 parts byweight of the polymerizable monomer (a)

are specifically described, but the present invention is not intended tobe limited to these Examples. Test methods for evaluating performancesof the dental curable composition prepared in each of Examples andComparative Examples are as follows.

(1) Crack Confirmation Test

Objective: Evaluation of strain in production of large-sized block curedbody

Method: an aluminum alloy mold was filled with a curable composition,sandwiched between nylon films at the top and bottom, and subjected topressure-welding by an aluminum alloy flat panel. Thereafter, hot presswas conducted using a hot press machine (manufactured by Shofu Inc.)under conditions of a press pressure of 2 t, a press plate temperatureof 100° C. and a press time of 30 minutes to provide a block cured bodyof φ100×14 mm. The operation was repeatedly conducted five times toproduce five block cured bodies. Each of the block cured bodies wasvisually observed, and a case where even one crack was generated wasdefined as “Present” and a case where no cracks were observed wasdefined as “Absent.”

(2) Bending Strength Test

Objective: Evaluation of bending strength of test specimen cut out fromblock cured body

Method: an aluminum alloy mold was filled with a dental curablecomposition, sandwiched between nylon films at the top and bottom, andsubjected to pressure-welding by an aluminum alloy flat panel.Thereafter, hot press was conducted using a hot press machine(manufactured by Shofu Inc.) under conditions of a press pressure of 2t, a press plate temperature of 95° C. and a press time of 10 minutes,to provide a block cured body of 12×14×18 mm. The block cured body wascut using a precision cutting machine to test pieces of 18×2×2 mm, andthereafter the surfaces of the test pieces were buffed to therebyprovide test specimens (five specimens were produced). The test wasperformed using a universal tester at a distance between supportingpoints of 10 mm and a crosshead speed of 1.0 mm/min, for evaluation bythe average of the results of the five test specimens.

(3) Weight-Drop Test

Objective: Evaluation of impact resistance of test specimen cut out fromblock cured body

Method: a block cured body of 12×14×18 mm was produced in the samemanner as in the bending strength test. The block cured body was cutusing a precision cutting machine to test pieces of 12×14×2 mm, andthereafter the surfaces of the test pieces were buffed to therebyprovide test specimens (ten specimens were produced). Each of the testspecimens was placed on a stainless-steel stage and a stainless-steelspherical body having a weight of 110 g was freely dropped from a heightof 3 cm. When no change was observed with respect to each of the testspecimens, the drop height was increased by 1 cm, and a drop distance atwhich cleavage or breaking occurred in each of the test specimens wasdefined as the distance at breaking, and evaluated by the average of theresults of the ten test specimens.

Compounds used in Examples of the present invention and abbreviationsthereof are shown below.

UDMA: urethane dimethacrylateBis-GMA: 2,2-bis(4-(3-(meth)acryloyloxy-2-hydroxypropoxy)phenyl)propaneTEGDMA: triethylene glycol dimethacrylateBPO: benzoyl peroxideR-972: Aerosil R-972 (manufactured by Nippon Aerosil Co., Ltd.)γ-MPS: γ-methacryloxypropyl trimethoxysilaneThe catalogue values of the average particle size, the pore volume andthe BET specific surface area of each silica filler are shown inTable 1. Silica fillers (1) and (2) were each appropriately subjected toa silane treatment and used for preparation of a dental composition.

TABLE 1 Average Pore BET specific particle size volume surface area (μm)(mL/g) (m²/g) Silica filler 0.9 — 4 (1) Silica filler 5-7 0.3 150 (2)

Each of resin compositions (I1 to 19) was prepared at each compositionshown in Table 2.

TABLE 2 Amount to be compounded (g) Resin (c) Polymerization composition(a) Polymerizable monomer initiator (d) Chain transfer agent No. UDMABis-GMA TEGDMA BPO α-Terpinene β-Terpinene γ-Terpinene I1 70 30 0.3 0.5I2 70 30 0.3 0.5 I3 70 30 0.3 0.5 I4 70 30 0.3 0.5 I5 70 30 0.3 0.1 I670 30 0.3 0.3 I7 70 30 0.3 1 I8 70 30 0.3 I9 70 30 0.3

Each of the resin compositions recited in Table 2 was used to prepareeach of curable compositions (Examples 1 to 7 and Comparative Examples 1and 2) according to each composition in Table 3. Each of the curablecompositions was used to produce each block cured body, and the crackconfirmation test was performed. The results are shown in Table 3.

TABLE 3 (b) Filler Silica filler (1) Silica filler (2) treated withtreated with Resin composition Presence of silane silane R-972 I1 I2 I3I4 I8 I9 cracks Example 1 30 2 68 Absent Example 2 70 2 28 AbsentExample 3 85 2 13 Absent Example 4 70 2 28 Absent Example 5 70 2 28Absent Example 6 70 2 28 Absent Example 7 70 2 28 Absent Comparative 702 28 Present Example 1 Comparative 70 2 28 Present Example 2

Examples 1 to 3 were each a system in which resin composition I1, towhich a-terpinene was added as the chain transfer agent, was used andthe amount of the filler (b) to be added was changed. A block cured bodyof φ100×14 mm could be produced without any cracks generated, even by adental curable composition in which the amount of the filler to be addedwas increased.

Example 4 was a system in which resin composition I1, to whichα-terpinene was added as the chain transfer agent, was used and the typeof the filler (b) was changed. A block cured body of φ100×14 mm could beproduced without any cracks generated, even when the type of the fillerwas changed.

Example 5 was a system in which while a-terpinene was added as the chaintransfer agent, resin composition 12, in which a portion of thepolymerizable monomer was changed as compared with resin composition I1,was used. A block cured body of φ100×14 mm could be produced without anycracks generated, even when the type of the polymerizable monomer (a)was changed.

Examples 6 and 7 were each a system in which each of resin compositions13 and 14, in which the type of the chain transfer agent was β-terpineneand γ-terpinene, respectively, was used. A block cured body of φ100×14mm could be produced without any cracks generated, even when the type ofthe chain transfer agent was changed.

Comparative Examples 1 and 2 were each a system in which each of resincompositions 18 and 19, in which no chain transfer agent was added intothe resin composition, was used. Cracking was generated due to no chaintransfer agent included in each of the curable compositions inproduction of each block cured body.

Next, each of the resin compositions recited in Table 2 was used toprepare each of curable compositions (Examples 8 to 11 and ComparativeExample 3) according to each composition in Table 4. Each of the curablecompositions was used to produce each block cured body, and thereafterthe bending strength test and the weight-drop test were performed. Theresults are shown in Table 4.

TABLE 4 (b) Filler Bending Distance at Silica filler (2) treated Resincomposition strength breaking with silane R-972 I5 I6 I4 I7 I8 (MPa)(cm) Example 8 70 2 28 198 14.5 Example 9 70 2 28 192 15.9 Example 10 702 28 199 17.6 Example 11 70 2 28 161 15.4 Comparative 70 2 28 196 13.3Example 3

Examples 8 to 11 were each a system in which the curable compositionprepared by the resin composition, in which the amount of the chaintransfer agent to be added was changed, was used. An increase in theamount of the chain transfer agent to be added increased the distance atbreaking by the weight-drop test of the block cured body produced, toenhance the impact resistance. In Examples 11, the curable compositionprepared by the resin composition, in which the amount of the chaintransfer agent to be added was larger than those in Examples 8 to 10,was used and therefore the bending strength was slightly deterioratedand the distance at breaking was also shortened.

In Comparative Example 3, the curable composition including no chaintransfer agent in the resin composition was used, and therefore crackswere generated in production of the block cured body and the distance atbreaking by the weight-drop test was also shorter than those in Examples8 to 11.

Next, Examples of the dental curable composition of the presentinvention, in which

the polymerizable monomer (a) was a monofunctional polymerizable monomerhaving a boiling point of 50 to 200° C., andthe filler (b) was a non-crosslinkable (meth)acrylate polymerare specifically described, but the present invention is not intended tobe limited to these Examples. Test methods for evaluating performancesof the dental curable composition prepared in each of Examples,Reference Examples and Comparative Examples are as follows.

Compounds used in Examples of the present invention and abbreviationsthereof are shown below.

(a: monofunctional polymerizable monomer having a boiling point of 50 to200° C.)MMA: methyl methacrylate, boiling point: 101° C.NBMA: n-butyl(meth)acrylate, boiling point: 162° C.(b: non-crosslinkable (meth)acrylate polymer)PMMA (1): polymethyl methacrylate powder, D50 average particle size: 50μm; weight average molecular weight: 800000PMMA (2): polymethyl methacrylate powder, D50 average particle size: 100μm; weight average molecular weight: 800000PEMA: polyethyl methacrylate powder, D50 average particle size: 50 μm;weight average molecular weight: 800000PMMA (3): polymethyl methacrylate powder, D50 average particle size: 500μm; weight average molecular weight: 2000000(c: polymerization initiator)BPO: benzoyl peroxide(d: chain transfer agent)α-terpineneβ-terpineneγ-terpinenelimonene(e) polymerizable monomer other than (a)EMA: ethylene dimethacrylate, boiling point: 260° C.

The test method and the evaluation method of each test are shown below.

(1) Confirmation Tests of Cracks and Foaming, and Local Shrinkage

Objective: Evaluation of cracks and foaming, and deformation inproduction of large-sized molded product using dental curablecomposition

Method: an aluminum alloy mold was filled with a dental curablecomposition in which a powder material and a liquid material wereadmixed (admixing ratio: monomer prepared/polymer=40/60), and sandwichedbetween nylon films at the top and bottom and subjected topressure-welding by an aluminum alloy flat panel. Thereafter, hot presswas conducted using a hot press machine (manufactured by Shofu Inc.)under conditions of a press pressure of 2 t, a press plate temperatureof 80° C. and a press time of 30 minutes to provide a cured body ofφ100×20 mm. The operation was repeatedly conducted five times to producefive cured bodies. Each of the cured bodies was visually observed, andthe degrees of cracks or inner foaming, and deformation were rated on a4-point scale: ⊙: very good; ◯: slightly good; Δ: slightly problematic,but not problematic clinically; and x: problematic and incapable ofbeing used clinically.

(2) Bending Strength

A molded body was cut to a size of 4 mm×4 mm×14 mm, a load was appliedto the center portion thereof using a universal tester at a crossheadspeed of 1 mm/min to measure the load at fracture, measuring thethree-point bending strength. The number of samples was six, and theaverage of the results thereof was determined. The bending strength wasclinically preferably 80 MPa or more, further preferably 100 MPa ormore.

The method for producing a resin material for dental cutting andmachining was as follow: (a), (c), (e), and (d) were mixed at acompounding ratio recited in Table 1 to provide a liquid component, and(b) and (f) were mixed to provide a powder component; the liquidcomponent and the powder component were mixed so that the compoundingratio recited in Table 1 was obtained, and an artificial tooth-shapedmold was filled with the resulting mixture and heated at 100° C. for 1minute; and the resultant was left to be cooled to provide a resinmaterial for dental cutting and machining.

TABLE 5 Example Example Example Example Example Example Composition 1213 14 15 16 17 Example 18 Example 19 (a) MMA 100 100 100 100 100 100 100100 (e) EMA (b) PMMA (1) 200 100 190 PMMA (2) 200 100 200 200 200 200(f) FASG 10 (c) BPO 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 (Outer percentage)(d) α- 0.5 0.5 0.5 0.5 (Outer Terpinene percentage) β- 0.5 Terpinene γ-0.1 0.3 0.5 Terpinene Total 300.7 300.7 300.7 300.7 300.7 300.3 300.5300.7 Test items Cracks ⊙ ⊙ ⊙ ⊙ ⊙ ⊙ ◯ ⊙ Foaming ◯ ⊙ ◯ ◯ ⊙ ⊙ ⊙ ⊙ Local ◯◯ ◯ ◯ ⊙ ◯ ⊙ ⊙ shrinkage Bending 121 126 131 110 140 141 125 132 strength[Mpa] Comparative Composition Example 20 Example 21 Example 22 Example23 Example 24 Example 25 Example 4 (a) MMA 100 100 100 100 100 100 (e)EMA 10 20 20 20 100 (b) PMMA (1) 100 PMMA (2) 200 200 200 300 200 200(f) FASG (c) BPO 0.2 0.2 0.2 0.2 0.2 0.2 0.2 (Outer percentage) (d) α-(Outer Terpinene percentage) β- Terpinene γ- 3 1 0.5 0.5 0.5 0.5Terpinene Total 303.2 311 320.7 220.7 420.7 300.7 300.2 Test itemsCracks ⊙ ◯ ◯ ⊙ ⊙ X ◯ Foaming ⊙ ⊙ ⊙ ◯ ⊙ ⊙ X Local ⊙ ◯ ⊙ ⊙ ⊙ X Δ shrinkageBending 85 113 118 116 121 141 134 strength [Mpa] (parts by weight)

From the above results, the resin material in Comparative Example 4,when not including Component (d), cannot be clinically used because ofbeing large in foaming; and the resin material in Example 25, in whichthe boiling point of Component (a) is high, can withstand use, but islarger in cracks and local shrinkage.

[Composite Resin Artificial Tooth]

Next, Examples of the composite resin artificial tooth of the presentinvention which is a composite resin artificial tooth having a monolayeror multilayer structure, in which a composite resin layer thereofincludes

(a) a polymerizable monomer,(b) a filler,(c) a polymerization initiator, and(d) a chain transfer agent, as well asthe composite resin artificial tooth of the present invention, which isconfigured fromat least one layer configured from a composite resin layer including(a) a polymerizable monomer,(b) a filler,(c) a polymerization initiator, and(d) a chain transfer agent, andat least one layer including a base layer that can chemically adhere toa denture base, configured from an acrylic resin layer including(e) a monofunctional (meth)acrylate polymerizable monomer,(f) a non-crosslinkable (meth)acrylate polymer,(c) a polymerization initiator, and(d) a chain transfer agentare specifically described, but the present invention is not intended tobe limited to these Examples. Test methods for evaluating performancesof the composite resin artificial tooth prepared in each of Examples andComparative Examples are as follows.

(1) Bending Test

Objective of evaluation: To evaluate bending strength of a test specimenobtained by molding a composite resin composition.

Evaluation Method:

After a stainless-steel mold (25×2×2 mm: cuboid type) was filled withthe composite resin composition prepared, molding with pressure andheating was conducted under conditions of a mold press pressure of 3 t,a molding temperature (base layer) of 100° C. and a molding temperature(enamel layer) of 120° C., and a press time of 10 minutes. Thereafter, amolded product was taken out from the mold, and then immersed in waterat 37° C. for 24 hours to provide a test specimen.

In the bending test, an Instron universal tester (Instron 5567manufactured by Instron) was used to measure the bending strength at adistance between supporting points of 20 mm and a crosshead speed of 1mm/min.

(2) Non-Defective Molded Product Test

Objective of Evaluation:

To evaluate molding properties of a molded product having a bilayerstructure (acrylic resin composition and composite resin composition)formed using a simulated artificial tooth mold (bilayer structure inwhich a base acrylic resin layer and a composite resin layer each havinga thickness differing in a transitive manner were stacked: FIG. 1).

Evaluation Method:

The acrylic resin composition was packed in the base layer differing inthickness in a transitive manner located on the lower portion of thesimulated artificial tooth mold (10 mm×10 mm×5 mm) illustrated in FIG.1, and thereafter molding with pressure and heating was conducted.Thereafter, the composite resin composition was packed in the compositeresin layer differing in thickness in a transitive manner located on theupper portion of the acrylic resin layer cured, and thereafter moldingwith pressure and heating was conducted. One hundred of the moldedbodies were produced, and cracking, chips, and the like generated in thesimulated artificial tooth were confirmed to thereby evaluate moldingproperties. Herein, the molding with pressure and heating was conductedunder conditions of a mold press pressure of 3 t, a molding temperature(base layer) of 100° C. and a molding temperature (composite resinlayer) of 120° C., and a press time of 10 minutes. As a result, a moldedproduct without any defects such as cracking and chips at all wasdefined as a non-defective product, and the non-defective rate wascalculated. A non-defective rate of 90 parts or more is defined to fallwithin the relevant range.

(3) Interface Adhesion State Confirmation Test

Objective of Evaluation:

To evaluate the influence on the interface (adhesion surface of baselayer and composite resin layer) in application of a forced pressureload to a molded product having a bilayer structure (acrylic resincomposition and composite resin composition) formed using a simulatedartificial tooth mold (bilayer structure in which a base acrylic resinlayer and a composite resin layer each having a thickness differing in atransitive manner were stacked: FIG. 1).

Evaluation Method:

Ten were randomly taken out from 100 of the simulated artificial teethdetermined as a non-defective product by the non-defective moldedproduct test, and were used as test specimens. The compressionresistance (pressure test) of each of the test specimens was measuredusing an Instron universal tester (Instron 5567 manufactured byInstron). The pressure direction of each of the test specimens isindicated in FIG. 2. A measurement condition was as follows: crossheadspeed: 1 mm/min; and the influence on the interface at a displacement of0.5 mm was observed and evaluated.

The rating criteria were as follow: ◯: not changed; Δ: partiallyclouded; and x: clouded at the entire interface or separated at theinterface.

Compounds used in Examples of the present invention and abbreviationsthereof are shown below.

(a) polymerizable monomerUDMA: urethane dimethacrylateBis-GMA: 2,2-bis(4-(3-(meth)acryloyloxy-2-hydroxypropoxy)phenyl)propaneTEGDMA: triethylene glycol dimethacrylate(b) fillersilica: average particle size: 0.9 μm; BET specific surface area: 4.0m²/g, treated with silane by γ-methacryloxypropyl trimethoxysilane andused for preparing composition.(c) polymerization initiatorBPO: benzoyl peroxide(e) monofunctional (meth)acrylate polymerizable monomer MMA: methylmethacrylate(f) non-crosslinkable (meth)acrylate polymer PMMA: polymethylmethacrylate, 50-part average particle size: 50 μm(d) chain transfer agentα-terpineneβ-terpineneγ-terpinene

Each of acrylic resin compositions (B1 to B9 and BC1) was preparedaccording to each composition shown in Table 6.

TABLE 6 Amount to be compounded (parts by weight) Liquid material (e)Powder material Monofunctional Acrylic (f) (meth)acrylate (c) resinNon-crosslinkable polymerizable Polymerization (d) composition(meth)acrylate polymer monomer initiator Chain transfer agent No. PMMAMMA BPO α-Terpinene β-Terpinene γ-Terpinene B1 65.0 35.0 0.04 0.04(0.11) (0.11) B2 65.0 35.0 0.30 0.04 (0.10) (011) B3 65.0 35.0 0.30 0.04(0.10) (0.11) B4 65.0 35.0 0.30 0.04 (0.10) (0.11) B5 65.0 35.0 0.500.04 (0.14) (0.11) B6 65.0 35.0 1.50 0.04 (4.30) (0.11) B7 65.0 35.00.30 0.03 (0.10) (0.09) B8 65.0 35.0 0.30 0.15 (0.10) (0.43) B9 65.035.0 0.30 0.40 (0.10) (1.14) BC1 65.0 35.0 0.50 (0.14) (Note) Admixingratio of powder material/liquid material: 65/35 (weight ratio). (Note)In Table, values in brackets are part(s) by weight based on 100 parts byweight of monofunctional (meth)acrylate polymerizable monomer.

Each of composite resin compositions (E1 to E11 and EC1) was preparedaccording to each composition shown in Table 7.

TABLE 7 Amount to be compounded (parts by weight) Composite (a) (c)resin Polymerizable monomer (b) Polymerization (d) composition Bis-Filler initiator Chain transfer agent No. UDMA GMA TGDMA Silica fillerBPO α-Terpinene β-Terpinene γ-Terpinene E1 49 21 30 0.21 0.40 (0.33)(0.44) E2 42 18 40 0.20 0.20 (0.33) (0.33) E3 21 9 70 0.10 0.10 (0.33)(0.33) E4 42 18 40 0.20 0.20 (0.33) (0.33) E5 42 18 40 0.40 0.20 (0.67)(0.33) E6 42 18 40 3.00 0.20 (5.00) (0.33) E7 42 18 40 0.30 0.20 (0.50)(0.33) E8 42 18 40 0.20 0.20 (0.33) (0.33) E9 42 18 40 0.20 0.06 (0.33)(0.10) E10 42 18 40 0.20 0.60 (0.33) (1.00) E11 42 18 40 0.20 1.00(0.33) (1.67) EC1 42 18 40 0.20 (0.33) (Note) In Table, values inbrackets are part(s) by weight based on 100 parts by weight ofmonofunctional (meth)acrylate polymerizable monomer.

Each of the composite resin compositions prepared was used to performthe bending test. The results are shown in Table 8.

TABLE 8 Composition Bending No. strength (MPa) Remarks Composite resinE1 112 composition E2 136 E3 156 E4 149 E5 151 E6 148 E7 133 E8 132 E9140 E10 145 E11 129 EC1 — Not tested due to incorporation of many gasbubbles and cracks

Composite resin compositions E1 to E3 were each a system in which theamount of the filler being Component (b) to be compounded was changed.As the amount of the filler (b) was increased, the bending strength washigher.

Composite resin compositions E2 and E4 were each a system in which thetype of the polymerizable monomer (a) (UDMA or Bis-GMA) was partiallychanged. While the same type of the chain transfer agent and the sameamount thereof to be compounded were adopted, the difference in the typeof the polymerizable monomer affected to cause a small difference inbending strength, but sufficient bending strength was exhibited.

Composite resin compositions E2, E5 and E6 were each a system in whichthe amount of the polymerization initiator (c) to be compounded waschanged. The same type and the same amount of the chain transfer agentwere adopted, and the bending strength was exhibited at the same levelas one another without any influence.

Composite resin compositions E2, E7 and E8 were each a system in whichwhile the amount of the chain transfer agent (d) to be compounded wasthe same as one another, the type (γ-terpinene, α-terpinene,β-terpinene) thereof was changed. The bending strength was exhibited atthe same level as one another without any influence even by the changein the type of the chain transfer agent.

Composite resin compositions E2, E9, E10 and E11 were each a system inwhich the amount of the chain transfer agent (d) to be compounded waschanged. When the amount of the chain transfer agent to be compoundedwas in the range from 0.06 (E9) to 0.6 (E10) parts by weight, thebending strength was exhibited at the same level as one another withoutany influence, but when the amount was 1.0 (E11) part by weight, thebending strength was found to be slightly deteriorated.

Composite resin composition EC1, without the chain transfer agent (d)compounded therein, caused many gas bubbles to be incorporated, and alsocaused cracks to be generated, and therefore a bending test specimencould not be produced therefrom.

Next, each of the composite resin compositions and the acrylic resincompositions prepared was used to perform the non-defective moldedproduct test and the interface adhesion state confirmation test. Theresults are shown in Table 9.

TABLE 9 Non-defective molded product test Main defective rate InterfaceComposition No. Non- (parts) adhesion state Acrylic resin Compositeresin defective Gas confirmation composition composition rate (parts)Cracks bubble test Example 26 B4 E1 92 4 0 ◯ Example 27 B4 E2 94 2 0 ◯Example 28 B4 E3 98 1 0 ◯ Example 29 B4 E4 92 4 0 ◯ Example 30 B1 E6 963 0 ◯ Example 31 B4 E7 94 3 0 ◯ Example 32 B4 E8 94 4 0 ◯ Example 33 B5E9 100 0 0 ◯ Example 34 B5 E10 96 2 0 ◯ Example 35 B2 E2 94 3 0 ◯Example 36 B3 E2 96 1 0 ◯ Example 37 B7 E5 94 3 0 ◯ Example 38 B8 E5 981 0 ◯ Example 39 B9 E2 96 3 0 ◯ Example 40 B9 E11 92 2 0 ◯ Example 41 B4E11 92 3 0 ◯ Comparative B4 EC1 16 45 74 X Example 5 Comparative BC1 EC18 55 81 X Example 6

As shown in Table 9, in each of Examples 26 to 41, the acrylic resincomposition and the composite resin composition, to which the chaintransfer agent was compounded, were used to form a simulated artificialtooth. As a result, while no generation of gas bubbles was observed atall, cracks were partially, but extremely slightly generated, and thenon-defective rate was 90 parts or more in each case. In addition, thesimulated artificial tooth as a non-defective product was used toperform the interface adhesion state confirmation test, and as a result,it was confirmed that there was no problem at the interface and the twocompositions adhered firmly.

As shown in Table 9, in each of Comparative Example 5 and ComparativeExample 6, the composite resin composition to which the chain transferagent was not compounded was used to form a simulated artificial tooth.In each case, gas bubbles and cracks were generated too much to enable asimulated artificial tooth to be formed, and the non-defective rate wasas very low as 16 parts in Comparative Example 5 and 8 parts inComparative Example 6. Any specimens being a non-defective product weretaken out therefrom and subjected to the interface adhesion stateconfirmation test, and as a result, it was confirmed that the entireinterface on which the two compositions adhered was clouded or separatedand dropped in all the specimens.

The chain transfer agent was compounded to the composition of thecomposite resin artificial tooth to thereby enable uniformpolymerization and curing, deterioration in material properties due tocompounding of the chain transfer agent was not observed, and shrinkageto be locally generated, cracking, clouding and chips were suppressed toachieve excellent physical properties.

Next, Examples of the resin artificial tooth of the present inventionincluding

(a) a monofunctional polymerizable monomer having a boiling point of 50to 200° C.,(b) a non-crosslinkable (meth)acrylate polymer,(c) a polymerization initiator, and(d) a chain transfer agentare described in detail, but the present invention is not intended to belimited to these Examples. Test methods for evaluating performances ofthe resin artificial tooth prepared in each of Examples, ReferenceExamples and Comparative Examples are as follows.

(1) Crack and Foaming Confirmation Test

Objective: Evaluation of cracks, inner foaming and local shrinkage ofresin composition in molding

Method: a liquid material composition and a powder material compositionwere admixed in the compounding ratio of each of Examples, the admixturewas filled in an aluminum alloy mold (cavity portion: 10 mm×10 mm×10mm), and thereafter a nylon film was interposed from above forpressure-welding by an aluminum alloy flat panel. Thereafter, hot presswas conducted using a hot press machine (manufactured by Shofu Inc.)under conditions of a press pressure of 2 t, a press plate settingtemperature of 100° C. and a press time of 10 minutes to provide a curedbody of 10 mm×10 mm×10 mm.

The cured body was visually observed, and “cracks” or “inner foaming,”and “local shrinkage” were rated at a 4-point scale (⊙: very good; ◯:slightly good; Δ: slightly problematic, but not problematic clinically;and x: problematic and incapable of being used clinically), and anycured body rated as ⊙ to Δ was defined as a non-defective product. Thenon-defective rate is desirably 90 parts or more.

(2) Surface Hardness Test

Objective: Evaluation of surface hardness (physical property) of resincomposition in molding

Method: the surface hardness of the cured body formed in the crack andfoaming confirmation test (1) above was measured using a Vickershardness meter. The surface hardness was measured at five points and theaverage was calculated.

A hardness of 15 or more, preferably 18 or more, is defined to fallwithin the relevant range of the resin artificial tooth.

Compounds used in Examples of the present invention and abbreviationsthereof are shown below.

(a) monofunctional polymerizable monomer having a boiling point of 50 to200° C.MMA (methyl methacrylate), boiling point: 101° C.(b) non-crosslinkable (meth)acrylate polymerPMMA (1) (polymethyl methacrylate powder), average particle size (D50):50 μm; weight average molecular weight: 800000PMMA (2) (polymethyl methacrylate powder), average particle size (D50):100 μm; weight average molecular weight: 800000(c) polymerization initiatorBPO: benzoyl peroxide(d) chain transfer agentα-terpineneβ-terpineneγ-terpinene(e) polymerizable monomer other than (a)EMA: ethylene glycol dimethacrylate, boiling point: 260° C.(f) filler other than non-crosslinkable (meth)acrylate polymerFASG: fluoroaluminosilicate glass powder, average particle size (D50):10 μm

The method for producing an artificial tooth was as follow: (a), (c),(e) and (d) were mixed at a compounding ratio recited in Table 10 toprovide a liquid component, and (b) and (f) were mixed to provide apowder component; the liquid component and the powder component weremixed so that the compounding ratio recited in Table 10 was obtained,and an artificial tooth-shaped mold was filled with the resultingmixture and heated at 100° C. for 1 minute; and the resultant was leftto be cooled to provide an artificial tooth.

TABLE 10 Example Example Example Example Example Example Composition 4243 44 45 46 47 Example 48 Example 49 (a) MMA 100 100 100 100 100 100 100100. (e) LMA (b) PMMA (1) 200 100 190 PMMA (2) 200 100 200 200 200 200(f) FASG 10 (c) BPO 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 (Outer percentage)(d) α- 0.5 0.5 0.5 0.5 (Outer Terpinene percentage) β- 0.5 Terpineneγ-Terpinene 0.1 0.3 0.5 Total 200.7 300.7 300.7 300.7 300.7 300.3 300.5300.7 Test items Cracks ⊙ ⊙ ⊙ ⊙ ⊙ ⊙ ◯ ⊙ Foaming ◯ ⊙ ◯ ◯ ⊙ ⊙ ⊙ ⊙ Local ◯◯ ◯ ◯ ⊙ ◯ ⊙ ⊙ shrinkage Vickers 20.3 19.7 20.1 19.8 19.7 20.4 20 19.9hardness Comparative Composition Example 50 Example 51 Example 52Example 53 Example 54 Example 55 Example 7 (a) MMA 100 100 100 100 100100 (e) LMA 10 20 20 20 100 (b) PMMA (1) 100 PMMA (2) 200 200 200 300200 200 (f) FASG (c) BPO 0.2 0.2 0.2 0.2 0.2 0.2 0.2 (Outer percentage)(d) α- (Outer Terpinene percentage) β- Terpinene γ-Terpinene 3 1 0.5 0.50.5 0.5 Total 303.2 311 320.7 220.7 420.7 300.7 300.2 Test items Cracks⊙ ◯ ◯ ⊙ ⊙ X ◯ Foaming ⊙ ⊙ ⊙ ◯ ⊙ ⊙ X Local ⊙ ◯ ⊙ ⊙ ⊙ X Δ shrinkageVickers 16.7 20.1 19.9 203 19.7 17.2 20.2 hardness (parts by weight)

In each of Examples 42 and 43, the difference in the type of thenon-crosslinkable (meth)acrylate polymer (polymethyl methacrylatepowder) (b) was examined, and problematic defects such as cracks,foaming and local shrinkage were not observed even when any of thepolymethyl methacrylate powders was used.

Example 44 was a system in which a plurality of the non-crosslinkable(meth)acrylate polymers (polymethyl methacrylate powders) (b) werecombined and added, and foaming and local shrinkage were slightlyobserved and no cracks were observed.

In Example 45, a filler other than the non-crosslinkable (meth)acrylatepolymer being Component (b) was added as Component (f) to thenon-crosslinkable (meth)acrylate polymer (polymethyl methacrylatepowder) (b), and foaming and local shrinkage were slightly observed andno cracks were observed.

In each of Examples 43, 46 and 49, the difference in the type of thechain transfer agent was examined, and generation of cracks and foamingwere not observed even when any of the chain transfer agents was used.

In each of Examples 47, 48, 49 and 50, and Comparative Example 7, theamount of the chain transfer agent to be added was examined. Whilegeneration of cracks and local shrinkage were only slightly observed ineach of Examples 47, 48, 49 and 50, inner foaming was observed too muchin Comparative Example 7 because the chain transfer agent (d) was notadded.

Examples 51 and 52 were a system in which a polymerizable monomer otherthan Component (a) was added as Component (e) to the monofunctionalpolymerizable monomer. In each case, generation of cracks and localshrinkage were only slightly observed.

In each of Examples 53 and 54, the compounding ratio of the liquidmaterial composition to the powder material composition was examined. InExample 53, foaming was only slightly observed. In Example 54, it wasconfirmed that molding could be conducted without any problem.

With respect to the surface hardness (physical property) in each ofExamples 42 to 54 and Comparative Example 7, while the surface hardnesswas observed to tend to be slightly deteriorated in Example 50 in whichthe chain transfer agent (d) was added in an amount of 3 parts by weightbased on 100 parts by weight of Component (a), such deterioration wasconsidered not to be problematic and therefore it could be determinedthat there was no influence on the surface hardness (physical property)depending on the presence of addition of the chain transfer agent.

In Example 55, Component (a) was entirely replaced with Component (e) inthe component composition in each of Examples. In Example 55, cracks andlocal shrinkage were confirmed to be generated.

1. A dental curable composition comprising (a) a polymerizable monomerand (b) a filler in a weight ratio of 10:90 to 70:30, and comprising0.01 to 10 parts by weight of (c) a polymerization initiator and 0.001to 1 part by weight of (d) a chain transfer agent being a terpenoidcompound based on 100 parts by weight of the polymerizable monomer (a).2. The dental curable composition according to claim 1, wherein thechain transfer agent (d) is at least one of α-terpinene, β-terpinene andγ-terpinene.
 3. The dental curable composition according to claim 1,wherein the polymerizable monomer (a) is a monofunctional polymerizablemonomer having a boiling point of 50 to 200° C., and the filler (b) is anon-crosslinkable (meth)acrylate polymer.
 4. A resin material for dentalcutting and machining, wherein a dental curable composition according toclaim 1, is molded into a size of 1 to 350 cm³.
 5. A resin artificialtooth produced by a dental curable composition according to claim
 1. 6.A composite resin artificial tooth having a monolayer or multilayerstructure comprising a composite resin layer produced by a dentalcurable composition according to claim
 1. 7. The composite resinartificial tooth according to claim 6, wherein the composite resinartificial tooth has a multilayer structure, and the structurecomprises: at least one of the composite resin layer; and at least oneacrylic resin layer comprising: (e) a monofunctional (meth)acrylatepolymerizable monomer, (f) a non-crosslinkable (meth)acrylate polymer,(c) a polymerization initiator, and (d) a chain transfer agent.
 8. Thedental curable composition according to claim 2, wherein thepolymerizable monomer (a) is a monofunctional polymerizable monomerhaving a boiling point of 50 to 200° C., and the filler (b) is anon-crosslinkable (meth)acrylate polymer.
 9. A resin material for dentalcutting and machining, wherein a dental curable composition according toclaim 2, is molded into a size of 1 to 350 cm³.
 10. A resin artificialtooth produced by a dental curable composition according to claim
 2. 11.A composite resin artificial tooth having a monolayer or multilayerstructure comprising a composite resin layer produced by a dentalcurable composition according to claim
 2. 12. The composite resinartificial tooth according to claim 11, wherein the composite resinartificial tooth has a multilayer structure, and the structurecomprises: at least one of the composite resin layer; and at least oneacrylic resin layer comprising: (e) a monofunctional (meth)acrylatepolymerizable monomer, (f) a non-crosslinkable (meth)acrylate polymer,(c) a polymerization initiator, and (d) a chain transfer agent.